A consumable upgrade is a consumable item(typically elixir/magic potion) that grants permanent or temporary bonus to stats, attributes or points(such as skill points).

TypeA(stat potion): Stat-altering potion. Consuming it just adds X to stat, permanently. Typically only central character stats are allowed to be altered(such as Vitality/Strength/Energy) and secondary stats like Change to Find more Magic Items or Resistance to Cold spells are only temporary altered(by adding e.g. a 4minute bonus to specific global modifiers of the character).

TypeB(crafting consumable): Attribute-altering consumable item. Broadly defined this is an item, that when used can upgrade/replace/enhance/add specific or random attribute of an item.

TypeC(spell/skill consumable): Grants skill levels(temporary) or charges(limited skill ability) or buffs limited in duration(upgrade). Typically this is represented as stacks of items(Stack of "charged stones of Level 30 Spell X"), when used this consumable allows to cast desired spell or apply a buff.
The skill charges appear as integral part of character skill set/tree and gain all associated bonus(such as "+x% damage with cold spells").
Some games such as Diablo1, allow adding Skill/Spell levels permanently by reading books(+1 level), but this system is not recommended for balance reasons.